This invention relates to a method for preparing copolymers incorporating a triorganotin moiety. This invention further relates to a method for preparing tin-containing polymers which retain their biological activity over a longer period of time relative to prior art materials.
The biological activity of polymers containing at least one triorganotin moiety (R.sub.3 Sn--) is well known. U.S. Pat. No. 3,167,473 discloses polymers obtained by polymerizing triorganotin derivatives of ethylenically unsaturated acids, including acrylic, methacrylic, and vinylbenzoic acids. The resultant products are employed as the toxicant in antifouling marine coatings and in compositions applied to agricultural food crops for the purpose of protecting them against infestation by a variety of harmful organisms, particularly fungi.
In accordance with the teaching of the aforementioned U.S. Pat. No. 3,167,473 the triorganotin-containing polymers are obtained using conventional bulk, solution or emulsion polymerization techniques. The examples of this patent disclose emulsion and bulk polymerization.
It has now been found that the biological activity of a given organotin-containing polymer is strongly influenced by the manner in which the polymer is prepared. Specifically, superior results are achieved using polymers obtained by solution polymerization in non-aromatic liquid parafinnic hydrocarbons such as hexane, heptane and cyclohexane. The polymerization medium may optionally contain up to 50% by volume, based on total liquid hydrocarbons, of a liquid aromatic hydrocarbon such as toluene or xylene.